1. Unit 10 ~ Thermochemistry (Chapter 10) And you

2. 10-1 Introduction and Definitions (Section 10.1) Thermochemistry is the study of heat energy changes in chemical reactions. There are many reasons for knowing the heat of a reaction, two of which include: 1) Heat energy can be used for work and 2) safety considerations.

3. First Law of Thermodynamics Conservation of Energy: energy can neither be created nor destroyed, only transformed from one form to another. Similar to conservation of mass. Potential Energy (PE) = stored E due to position OR chemical composition. Kinetic Energy (KE) = E of motion. = ½ mv 2

4. Second Law of Thermodynamics Heat always flows from hot to cold (high temp to low temp). Heat E ≠ temperature Heat = how much energy is transferred from one sub. to another due to temp. difference Temperature is proportional to KE (½ mv 2 ). The higher the temperature, the greater the average velocity of the molecules. Temperature units: ºC or K

5. 10-2 Equation for Heat and Temperature (Section 10.2) The quantitative relationship between heat and temperature is: Q = (s) (m) (ΔT) Q = heat absorbed or lost+Q if abs., -Q if lost m = mass (in grams) ΔT = temperature change:ΔT = T final – T initial s = specific heat capacity( J/gºC) s = the amount of energy needed to raise the temp of 1 g of a substance by 1ºC.

6. H 2 O: s = 4.18 J/gºC(holds heat well) Gold:s = 0.13 J/gºC (transfers heat well) If 1 g of water and 1 g of Au raise 1ºC, which substance has stored more heat? The WATER!!!! This is why water is used to store energy!

7. Sample Problem: Determine the amount of energy (heat) in joules required to raise the temperature of 7.40 g of water from 29.0 ºC to 46.0 ºC.

8. Q = m ▲ T s Joules grams 0 C J/g 0 C = 7.40 (17.0) 4.18 Q = 525.844 = 526 Joules

9. Note how the amount of heat transferred depends upon the mass involved. This is why a drop of boiling water at 100ºC would hurt a bit on your palm, but a cup of boiling water at 100ºC poured on your hand would seriously burn!

10. Units of heat: 1 J ~ 1 heartbeat of E 4.18 Joules = 1 calorie calorie – E to raise the temp. of 1g of H 2 O 1 O C kcal – 1000 cal, used for food (1 apple = 100kcal) But called 100 Calories in nutrition labels!!! 1 Cal = 1000 cal = 1 kcal = 4.184 KJ kJ = 1000J, heat needed to raise ~1 Cup water 1 O C (1 cup ~ 237 ml)